Ramp feed antenna



J1me 1967 E. M. T. JONES ETAL 3,325,815

RAMP FEED ANTENNA Filed Feb. 18, 1964 1 VENTO pm a 5' 455%;- 55.52

United States Patent 3,325,815 RAMP FEED ANTENNA Edward M. T. Jones,Portola Valley, Robert L. Tanner,

Menlo Park, and Eugene D. Sharp, Palo Alto, Calif.,

assignors to the United States of America as represented by theSecretary of the Air Force Filed Feb. 18, 1964, Ser. No. 345,813 1Claim. (Cl. 343-731) This invention relates to an antenna fortransmitting or receiving radiant energy and, more particularly, to avery broad bandwidth antenna having an inherent direction selectivecharacteristic.

One of the disadvantages in the prior art resides in the narrowbandwidth over which an antenna may be operated thereby requiringdiffering physical variations depending upon the operating frequency orfrequencies.

The antenna of the present invention is used to couple electromagneticwaves into a region enclosed by two spaced conducting sheets. Theconducting sheets are connected by a ramp-like structure. One end of theramp terminates in the center conductor of a coaxial output cable whichis connected to one of the spaced sheets. The other end of the ramp isconnected to a termination resistor which is connected to the remainingspaced sheet. Depending upon the direction of the arrival of thereceived signal, the signal is fed either to the coaxial cable or to theterminating resistor where the signal is dissipated. Thus the antennahas an inherent direction selective characteristic. It is to be notedthat hereinafter the aforementioned structure is referred to as a rampfeed antenna.

One of the advantages of the ramp antenna of the present invention isthat it can be used over a very large frequency bandof the order of tenand twenty to one with input impedance being constant over this band.The radiation pattern of the ramp antenna is that of an endfire antennaof the same electrical length for a long electrical length the main lobeis narrow and for shorter electrical lengths the main lobe is wider.

An object of the present invention is to provide a broad band antennafor radiant energy having a pair of spaced conducting sheets with aramp-like structure connecting the sheets.

Another object of the present invention is to provide a broad bandantenna for radiant energy wherein electromagnetic waves are coupledinto a region enclosed by two conducting sheets.

Yet another object of the present invention is to provide a broad 'band,constant impedance antenna wherein electromagnetic waves are coupledinto a region enclosed by two conducting sheets and operating to providean endfire antenna radiation pattern.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and s ecific objects obtained with its use,reference should be had to the singly accompanying drawing anddescriptive matter in which is illustrated and described a preferredembodiment of the invention.

A schematic of the ramp feed antenna is shown in the single drawing. Itis named the ramp feed antenna because it resembles a ramp in the formof conductor 1 which extends from lower conducting sheet 2 to upperconducting Patented June 13, 1967 "ice sheet 3. Conductor 1 is referredto as the ramp feed and one end thereof is connected through terminatingresistor 4 to conducting sheet 3; the other end is connected to centerconductor 5 of coaxial transmission line 6 with outer conductor 7 ofcoaxial line 6 connected to conducting sheet 2. The ramp feed antennacan be used as a transmitting or receiving antenna.

Conducting sheets 2 and 3 are spaced and parallel. They may be in theform of solid conductors or of a wire mesh; their shape may be planar orcurved. It is also to be noted that they may be parallel to each otheror flared.

The ramp feed antenna may be comprised of one of a number ofconfigurations. For example, the ramp feed may be a single large orsmall conducting wire, it may be made up of several closely or Widelyspaced conducting wires; or it may 'be one or more conducting strips. Inany configuration, the ramp conductor or conductors are chosen so thatthe characteristic impedance of the ramp is constant along its lengthand the resistance of the terminating resistor is chosen to be equal tothe characteristic impedance.

When the ramp feed antenna illustrated in the single drawing isoperating in the receiving mode, electromagnetic waves incident uponramp feed antenna 1 induce currents in the antenna conductors 2 and 3.Depending upon the direction of arrival, the induced currents travel tothe output end, coaxial line 6 or to terminating resistor 4. When thewaves are coming from the right of the illustrated single drawing, theinduced currents travel to the output coaxial line 6, and can bedetected by a receiving system. When the waves are incident from theleft in the single illustrated drawing, the induced currents travel toterminating resistor 4, are dissipated there, and are not detected inthe receiving system. Thus the ramp fed antenna has an inherentdirection selectively of waves depending upon their direction ofarrival.

The principal advantage of the ramp feed antenna is that it can be usedover a very large frequency band with the input impedance 'beingconstant over this band. The radiation pattern of the ramp antenna isthat of an endfire antenna of the same electrical length; for a longelectrical length the main lobe is narrow and for shorter electricallengths the main lobe is wider.

The ramp feed antenna of the present invention was utilized in oneinstance in the 120 to 1200 me. band. The ramp feed antenna was arrangedto provide a characteristic impedance of ohms. The measured input VSWRof this antenna was less than 1.5 over a ten to one frequency band whena 75 ohm resistor was used as the terminating resistor.

Although the invention has been described with reference to thereception of radiant energy, it will be apparent to those skilled in theart that the antenna described herein may also be used for transmissionif desired.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be per-formed, we declarewhat we claim is:

In an electromagnetic antenna system with a ramp feed to provide broadband operations comprising a first and second conducting sheet in aspaced and parallel arrangement to each other, each of said first andsecond conducting sheets having comparable first and second ends, acoaxial line having inner and outer conductors, said outer conductor ofsaid coaxial line 'being connected to 3 4 said first conducting sheet inthe region of said first end References Cited thereof, a resistor havinga preselected impedance con- UNITED STATES PATENTS nected to said secondconducting in the region of said second end thereof, a third conductorinterconnecting 210951078 10/1937 PePeISOH 343-731 X said innerconductor of said coaxial line and said resistor, 5 3268896 8/1966 Spltz343 785 X said third conductor operating as a ramp feed and havingFOREIGN PATENTS a constant characteristic impedance along the lengththere- 1,160,096 7/1958 France of identical to said preselectedimpedance of said third conductor with said ramp feed receivingelectromagnetic HERMAN KARL SAALBACH, P i E i energy from one direction*for dissipation in said resistor 10 ELI LIBERMAN Examiner and receivingenergy from another direction for utiliza- {ion in aid oaxial line, R.COHN, S. CHATMON, JR., Assistant Examiners.

